Alternating Pattern of Stereochemistry in the Nonactin Macrocycle Is Required for Antibacterial Activity and Efficient Ion Binding

Abstract

Nonactin is a polyketide antibiotic produced by Streptomyces griseus ETH A7796. It is active against a range of Gram positive organisms, acting as an ionophore that has a high selectivity for K + ions. Among the polyketides, nonactin has a unique structure. It is a 32-membered, cyclic tetraester generated from four monomers of nonactic acid, two of which are (+)-nonactic acid and two of which are (−)-nonactic acid. The monomers are arranged (+)-(−)-(+)-(−) in the macrocycle so that nonactin has S4 symmetry and is achiral. As the structure of nonactin is unique, so is the biosynthesis of the compound. There is much evidence that after an early achiral intermediate, there are two mirror image biosynthesis pathways, one for the synthesis of each enantiomer of nonactic acid. Emerging evidence suggests that the two pathways arose from gene duplication followed by divergent evolution. The central question, therefore, raised by both the structure and the biosynthesis of nonactin concerns the benefit, if any, to the producing organism in initially selecting for, and then maintaining, two independent pathways for nonactic acid synthesis and for generating only the achiral diastereoisomer of nonactin.To understand why achiral nonactin is the naturally generated diastereoisomer we prepared through synthesis two alternate diastereoisomers of nonactin, one prepared solely from (+)-nonactic acid and one prepared solely from (−)-nonactic acid, referred to here as 'all-(+)-nonactin' and 'all-(−)-nonactin' respectively. Both all-(+)-nonactin and all-(−)-nonactin were more than 500-fold less active against Gram positive organisms than nonactin confirming that the biosynthesis of both nonactic acid enantiomers, and their incorporation into nonactin, is necessary for biological activity. To understand the lack of antibacterial activity we used isothermal calorimetry to measure the association constant K a , ΔG, ΔH and ΔS of formation for the K + , Na + and NH 4 + complexes of nonactin and all-(−)-nonactin. The natural diastereoisomer had a high selectivity for K + to which it bound approximately 880-fold better than all-(−)-nonactin. We used a picrate partitioning assay to confirm that all-(−)-nonactin, unlike nonactin, could not partition K + ions into organic solvent. To complement the thermodynamic data we used a simple experimental model to mimic ion transport. Using two concentric glass tubes we arranged for two aqueous samples to be separated by a CHCl 3 layer. By following the co-transport of picrate anion from one aqueous layer to the other, through the organic phase, we were able to measure the rates of K + transport that were facilitated by the ionophores. Whereas nonactin allowed for efficient K + transport, all-(−)-nonactin was completely nigel.priestley@umontana.edu. Supporting Information Available: 1 H and 13 C NMR spectra and mass spectra for compounds 8 to 17. This material is available free of charge via the Internet at

Inhibitory Effects of Macrotetrolides from Streptomyces spp. On Zoosporogenesis and Motility of Peronosporomycete Zoospores Are Likely Linked with Enhanced ATPase Activity in Mitochondria

“…A motility inhibitory compound, staurosporine has recently been found to successfully suppress development of downy mildew on treated grapevine leaves (Islam et al, 2011). Macrotetrolide antibiotics exhibit a very wide range of effects, ranging from antimicrobial to insecticidal, acaricidal, anticancer, antiprotozoan (coccidiostatic), immunosuppressive and antiparasitic (antihelminthic) (Meyers et al, 1965; Borrel et al, 1994; Zizka, 1998; Kusche et al, 2009). Plant growth promotion and exhibition of specific insecticidal effects of precursors of macrotetrolide antibiotics, nonactic and homononactic acids have been reported (Jizba et al, 1992).…”

Coordination polymer of copper with a silicon-containing Schiff base

“…The X-ray molecular structure of the Cu(II) complex, with the atom-numbering scheme, are shown in Figure 3 6.640 (8), as shown in Figure 3(b). Consequently, the environment of Cu atom can be characterized as a distorted (4 þ 2) coordination octahedron.…”

“…[1][2][3][4][5][6] Various architectures are constructed based on a variety of building blocks with different interactions. 7 Besides coordinative bonds that permit formation of compounds with a structural diversity, depending on the coordination geometry of the metallic ion, 8 other intermolecular interactions such as hydrogen bonds, C-HÁÁÁ or -interactions, van der Waals, and so on, [9][10][11] offer premises for the organization of individual molecules into well-defined supramolecular assemblies. [12][13][14][15][16][17] In recent years, noncovalent interactions and self-assembly phenomenon have attracted attention due to their use in sensors, photonic devices and catalysts, as well as in host-guest chemistry.…”

Pilot-plant cultivation of Streptomyces griseus producing homologues of nonactin by precursor-directed biosynthesis and their identification by LC/MS-ESI

“…6 Although there is no information about the biological activities of macrotetrolides B-G, 7 it was reported that the K + affinity was found to be highly correlated with the biological activity; for example, the association constant for the K + complex of dinactin is sevenfold higher than that of nonactin. 8 To study the biological activities of compounds containing bishomononactic acid and also higher homologues, that is tetranactin, macrotetrolides B-G (7,9,11,13), and nonnatural macrocyclic lactones, these compounds were prepared both by cultivation (see above) and by organic synthesis. 9 Macrotetrolide a was synthesized from two (À)-and two (+)-bishomononactic acids in seven steps 10 but the relevant papers do not mention any biological effects of this compound.…”

“…This natural nonactin has about 100-fold stronger antimicrobial activity against Bacillus anthracis, Enterococcus faecalis, Staphylococcus aureus or methicillin-resistant S. aureus than the synthetic all(+) or all(À) nonactin. 11 To prepare sufficient amounts of higher nonactin homologues for further biological studies, we optimized cultivation conditions on a pilot-plant scale including the use of precursor-directed biosynthesis (PDB) and identification of metabolites by liquid chromatography (LC)/MS-ESI.…”